... this definition of Tex/Mex food.
"Tex-Mex food might be described as native foreign food, contradictory through that term may seem, It is native, for it does not exist elsewhere; it was born on this soil. But it is foreign in that its inspiration came from an alien cuisine; that it has never merged into the mainstream of American cooking and remains alive almost solely in the region where it originated..."
---Eating in America, Waverly Root & Richard de Rochemont [William Morrow:New York] 1976 (p. 281)
For more interesting information on the culinary evolution with our neighbors to the south follow this link.
http://www.foodtimeline.org/foodmexican.html